Cultured human adipocytes precursors (HAPs) are a promising culture system for investigation of inherent differences in cellular metabolism in obesity and diabetes HAPs were established in culture from the stromal vascular fraction of collagenase digests of abdominal subcutaneous fat. HAPs were stimulated to initiate the differentiation process to mature adipocytes in vitro in the presence of insulin (5 x 10 to the minus eighth m), as assessed by triglyceride deposition. In order to study an acute action of insulin a method for measuring initial rates of glucose transport in confluent monolayers of HAPS was developed. The glucose transport system was chosen because insulin stimulation of the glucose transporter has been extensively investigated in mature adipocytes. Insulin stimulated glucose transport in HAPs with a mean (n=5) ED50 or 3x10 to the minus 9M insulin. Maximally stimulated rate (137.5 + or - 10.5nL/sec ng) was twice basal (63.4 + or - 9.8nL/sec ng). Mature adipocytes may still reflect the in vivo milieu at the time of biopsy. An actue action of insulin in HAPs has been defined that can now be compared to similar data obtained for mature adipocytes from thesame biopsy. Thus, tis system may provide a tool for distinguishing between environmentally and genetically determined alterations in cellular metabolism that contribute to the increased insulin resistance associated with obesity and diabetes.